To prevent health problems in pediatric population, the Russian Federation (RF) is implementing the Complex of measures to combat obesity in children under 18 years of age, approved on  December 1, 2023, No. 18824-P12-TG. The study aimed to consider body mass index (BMI) formation in Russian children and adolescents in the regional aspect. As part of the all-Russian monitoring of the physical development of children and adolescents in 2021–2024, BMI of 258,611 boys and 252,629 girls living in 50 constituent entities of the RF was studied. Big data analysis has shown that in most regions there is a harmonious development of the child population and the indicators fit into the BMI 25^th–75^th centile for the RF as a whole, which is 19.6–22.9 kg/m² in boys aged 17 and 18.7–22.3 kg/m² in girls. At the same time, there is an influence of socio-economic factors. The analysis of the regional features of BMI formation in children and adolescents aged 7–17 years has shown that BMI has a higher value, the lower the place of the subject of the RF in terms of gross regional product.